Doppler ultrasonic flowmeter

ABSTRACT

A Doppler type ultrasonic flowmeter has an ultrasonic transmitting means for emitting ultrasonic pulses from an ultrasonic transducer into a fluid pipe, a flow velocity profile measuring means for receiving an ultrasonic echo reflected from a measurement region in the fluid pipe thereby to measure a flow velocity profile of a fluid to be measured, a fluid flow rate computing means for calculating the flow rate thereof on the basis of the flow velocity profile of the fluid to be measured, and a frequency selecting and setting means for automatically selecting a fundamental frequency of an ultrasonic wave that causes a resonant transmission phenomenon to take place from the ultrasonic transducer. The frequency selecting and setting means controls the operation of the ultrasonic transmitting means such that an ultrasonic wave of a selected optimum frequency is emitted from the ultrasonic transducer. This arrangement makes it possible to provide a highly versatile Doppler type ultrasonic flowmeter that permits simple, easy, contactless, precise and highly accurate measurement of the flow rates of fluids to be measured that are flowing in various fluid pipes.

TECHNICAL FIELD

The present invention relates to a Doppler type ultrasonic flowmeter formeasuring a flow rate of a fluid to be measured by utilizing anultrasonic Doppler shift and, more particularly, to a Doppler typeultrasonic flowmeter that permits automatic adjustment and setting ofoptimum frequencies and optimum incident angles of ultrasonic waves.

BACKGROUND ART

Flowmeters for measuring flow velocities and flow rates of fluids to bemeasured that are passing in fluid pipes are roughly divided into twotypes according to measurement principles.

A first type of flowmeters measures flow rates by making use of the factthat the processing amount of a fluid flowing through a fluid pipechanges, depending upon flowing direction. As this type of flowmeter,there is an orifice flowmeter. The orifice flowmeter measures flow ratesby utilizing the fact that fluid pressure on upstream side of an orificediffers from that on the downstream side. This flow rate measuringmethod will be hereinafter referred to as “average value approximation.”

The second type of flowmeters is used for measuring flow rates of flowsprimarily in round pipes.

This type of flowmeters is adapted to measure a flow velocity at onepoint in the flow in a pipe, e.g., at a predetermined point on a pipeaxis, and then a flow velocity profile configuration in the pipe ispresumed from a theoretical value based on the obtained measurementvalue. The flow velocity profile configuration is integrated todetermine a flow rate. This flow rate measurement method will behereinafter referred to as “approximate integration.”

Meanwhile, some flowmeters are known as ultrasonic flowmeters formeasuring the flow rates of fluids by applying ultrasonic waves tofluids to be measured.

Such ultrasonic flowmeters are roughly divided into a type adapted tomeasure the flow rates by the average value approximation method and atype adapted to measure the flow rates by the approximate integration.

The ultrasonic flowmeters employing the average value approximationmeasure the flow rates by determining an average velocity between twopredetermined points by utilizing the fact that the time required for anultrasonic pulse to travel between the two predetermined points differsby the flow velocity of a fluid, depending on whether the ultrasonicpulse advances towards the upstream side of the flow of the fluid orconversely towards the downstream side of the flow.

The ultrasonic flowmeters employing the approximate integrationdetermines the velocity of a fluid to be measured at one point on thecentral axis of a pipe by utilizing the Doppler shift method thereby tomeasure the flow rate thereof on the basis of the determined velocity ofthe fluid, one of which has been disclosed in Japanese Patent Laid-openPublication No. HEI 6-294670. The ultrasonic flowmeter based on theapproximate integration determines a flow velocity profile configurationfrom a theoretical value or an empirical rule and then performsintegration. For instance, flow velocity profile in a laminar flowregion in a pipe is represented by a parabola, so that the flow ratescan be determined by using a fluid velocity measured on its central axisby using boundary conditions on a pipe wall. Strictly speaking, thistheoretical solution applies to a flow in a steady state, and therefore,the ultrasonic flowmeter based on the approximate integration can beapplied only to a flow of a steady state and cannot be used for the flowin non-steady state.

In general, the flow of a viscous fluid is widely known to berepresented by Navier-Stokes equation (hereinafter referred to as “NSequation”). A conventional ultrasonic flowmeter determines flow rates byutilizing the knowledge of flow distribution with respect to a steadystate, ignoring time derivative term of an NS equation. For this reason,if an object to be measured is a flow field (the flow field of a fluid)where the approximate integration does not hold due to time-dependentchanges in the flow rate, then measurement accuracy may be significantlydeteriorated or validity of measurement results may be damaged.

Such flow fields include, for example, a flow field in which a changetime of a flow rate system is shorter than the time required fordetermining an average flow rate, or a flow field in which a flow hasnot yet fully developed. In the former case, the time derivative term ofthe NS equation does not reach zero, while in the latter case,one-dimensional approximation of the NS equation does not hold.

The conventional flowmeters are for performing flow rate measurement insteady states, so that measuring flow rates with sufficient accuracyrequires, for example, an extremely long runway for stabilizing a flowon the upstream side of a measurement location. This requires time, costand labor to provide piping. In addition, since the flowmeters are formeasuring flow rates of flows in steady states, it has been difficult tomeasure flow rates of flows in non-steady states.

Furthermore, the conventional flowmeters are adapted to measure anaverage flow rate of a fluid passing in a closed pipe, such as a roundpipe, making it impossible to measure local flow rates of larger flowsystems. For instance, none of the flowmeters have been able to measurecharacteristic flow rates that vary with time in the vicinity of aninlet or outlet of a huge agitating tank.

The flow of a fluid to be measured in a flow field of athree-dimensional space is represented by a three-dimensional vectoramount, while a conventional flowmeter measures a flow rate, presuming aone-dimensional flow in a pipe. For this reason, even in a closed pipe,if a flow is three-dimensional, then flow rate measurement accuracyextremely deteriorates or the measurement becomes impossible. Forexample, immediately following a bent pipe, such as an elbow pipe or aU-shaped inversion pipe, the flow of a fluid turns to bethree-dimensional due to a centrifugal action. The conventionalflowmeter installed at such a location will not be able to performaccurate flow measurement.

The present inventors have proposed, in the description of JapanesePatent Application No. HEI 10-272359, a Doppler type ultrasonicflowmeter that utilizes ultrasonic Doppler shifts, and permits precise,time-dependent, contactless measurement of flow rates even if fluids tobe measured are in non-steady states.

The Doppler type ultrasonic flowmeter adopts a technique to therebydirectly calculate the flow rate from an instantaneous flow velocityprofile of the fluid to be measured in the fluid pipe, and it has beenfound to present high accuracy and responsiveness in measuring the flowrates of fluids to be measured.

The conventional Doppler type ultrasonic flowmeters are also required topermit measurement of flow rates of fluids to be measured in fluid pipeswith ease and great versatility.

In order to smoothly measure the flow velocities of fluids to bemeasured in various types of fluid pipes by Doppler type ultrasonicflowmeters, it is necessary to secure sufficient ultrasonic transmissionefficiency and to secure sufficient reflected wave S/N ratios for fluidpipes having various pipe wall thicknesses.

In the conventional Doppler type ultrasonic flowmeters, the ultrasonictransmission characteristics of a metal wall of the fluid pipe arechecked by changing the thickness of the metal wall so as to set anoptimum thickness of the fluid pipe.

However, application of the Doppler type ultrasonic flowmeters to anactual equipment makes it impossible to change the thickness of fluidpipes, and ultrasonic flowmeters having optimum ultrasonic transmissioncharacteristics for each type of the fluid pipes must be prepared,exhibiting poor versatility.

The present invention has been made, considering the circumstancesdescribed above, and it is a primary object of the present invention toprovide a highly versatile Doppler type ultrasonic flowmeter thatpermits simple, easy, contactless and accurate measurement of flow ratesof fluids to be measured in various fluid pipes.

Another object of the present invention is to provide a Doppler typeultrasonic flowmeter that automatically selects an optimum ultrasonicfrequency or an optimum ultrasonic incident angle that causes a resonanttransmission phenomenon to take place with respect to various wallthicknesses of fluid pipes so as to permit precise and accuratemeasurement of flow rates of fluids to be measured by utilizingultrasonic Doppler shifts.

A further object of the present invention is to provide a Doppler typeultrasonic flowmeter that permits accurate and precise measurement offlow rates even of opaque or translucent fluids to which optical flowrate measurement methods cannot be applied.

A still further object of the present invention is to provide a Dopplertype ultrasonic flowmeter that permits precise and accurate measurementof fluids to be measured in fluid pipes even if swirling flows or flowsnot parallel to pipes are produced in fluid pipes.

DISCLOSURE OF THE INVENTION

The objects of the present invention described above can be achieved byproviding a Doppler type ultrasonic flowmeter comprising an ultrasonictransmitting means provided with an ultrasonic transducer for emittingan ultrasonic pulse and adapted to direct the ultrasonic pulses from anultrasonic transducer into a fluid to be measured that is flowing in afluid pipe, a flow velocity profile measuring means for receiving anultrasonic echo of the ultrasonic pulse led into the fluid to bemeasured, the ultrasonic echo being reflected from a measurement regionin the fluid pipe, and measuring a flow velocity profile of the fluid tobe measured in the measurement region, a fluid flow rate computing meansfor calculating the flow rate of the fluid to be measured on the basisof the flow velocity profile of the fluid to be measured, and afrequency selecting and setting means for automatically selecting afundamental frequency of an ultrasonic wave from the ultrasonictransducer that causes a resonant transmission phenomenon to take placewith respect to the pipe wall of the fluid pipe, wherein the frequencyselecting and setting means controls the operation of the ultrasonictransmitting means so that an ultrasonic wave of a selected optimumfrequency is emitted from the ultrasonic transducer.

In order to solve the problems described above, in a preferredembodiment of the Doppler type ultrasonic flowmeter according to thepresent invention, the oscillation frequency selecting and setting meansautomatically adjusts and sets the oscillation frequency of anultrasonic pulse emitted from the ultrasonic transducer so that anintegral multiple of an ultrasonic half-wave length is equal to the wallthickness of the fluid pipe. The oscillation frequency selecting andsetting means comprises an oscillation amplifier for emitting anultrasonic wave of a required oscillation frequency from the ultrasonictransducer, an oscillation frequency changing device for variablyadjusting and setting an oscillation frequency of the oscillationamplifier, a frequency domain setting means for operating theoscillation frequency changing device in a frequency domain designatedbeforehand, an ultrasonic receiving means for receiving an ultrasonicecho of the ultrasonic pulse emitted from the ultrasonic transducer thatis reflected from the measurement region in the fluid pipe, and areflected wave intensity extracting means for extracting and storing theintensity of the received ultrasonic echo, wherein the oscillationfrequency selecting and setting means repeats an operation of extractingand selecting oscillation frequencies to automatically select an optimumultrasonic frequency.

The Doppler type ultrasonic flowmeter further comprises an incidentangle adjusting and setting means for adjusting and setting an incidentangle of an ultrasonic pulse emitted from the ultrasonic transducer intothe fluid to be measured, wherein the incident angle adjusting andsetting means has the ultrasonic transducer provided on the fluid pipeso as to be adjusted and set to provide the ultrasonic pulse with anincident angle that causes the resonant transmission phenomenon to takeplace with respect to the pipe wall of the fluid pipe, the frequencyselecting and setting means and the incident angle adjusting and settingmeans being combined.

Furthermore, in order to achieve the above objects, there is provided aDoppler type ultrasonic flowmeter in accordance with the presentinvention, which comprises an ultrasonic transmitting means providedwith an ultrasonic transducer for emitting ultrasonic pulses from anultrasonic transducer into a fluid to be measured that is flowing in afluid pipe, a flow velocity profile measuring means for receiving anultrasonic echo of the ultrasonic pulse led into the fluid to bemeasured that is reflected from the measurement region in the fluidpipe, and measuring a flow velocity profile of the fluid to be measuredin the measurement region, a fluid flow rate computing means forcalculating the flow rate of the fluid to be measured on the basis ofthe flow velocity profile of the fluid to be measured, and an incidentangle adjusting and setting means for adjusting and setting the incidentangle of an ultrasonic pulse emitted from the ultrasonic transducer intothe fluid to be measured, wherein the incident angle adjusting andsetting means has the ultrasonic transducer provided on the fluid pipesuch that it can be adjusted and set so as to provide the ultrasonicpulse with an incident angle that causes the resonant transmissionphenomenon to take place with respect to the pipe wall of the fluidpipe.

Furthermore, the incident angle adjusting means may be equipped with anultrasonic transducer provided on the fluid pipe from outside, anincident angle changing mechanism that permits adjustment and setting ofthe incident angle of an ultrasonic pulse emitted from the ultrasonictransducer, an incident angle range setting means for actuating theincident angle changing mechanism within the range of an incident anglerange designated beforehand, and a reflected wave intensity extractingmeans for receiving the ultrasonic echo of the ultrasonic wave emittedfrom the ultrasonic transducer that is reflected from the measurementregion in the fluid pipe and extracting and storing the intensity of theultrasonic echo, wherein the incident angle adjusting and setting meansmay repeatedly perform an operation for extracting and selectingultrasonic pulse incident angles to automatically select an optimumultrasonic pulse incident angle. The ultrasonic transducer may beprovided on the outer side of the fluid pipe such that the mountingangle thereof can be adjusted, and the mounting angle of the ultrasonictransducer may be selected by the incident angle changing mechanism soas to adjust and set the incident angle of an ultrasonic pulse emittedfrom the ultrasonic transducer.

Furthermore, in order to achieve the above objects, the Doppler typeultrasonic flowmeter according to the present invention comprises afirst ultrasonic transducer provided on a fluid pipe, a secondultrasonic transducer provided apart from the first ultrasonictransducer in the axial direction of the fluid pipe, an ultrasonictransducer moving mechanism for relatively moving the first ultrasonictransducer forward or backward with respect to the second ultrasonictransducer, the two ultrasonic transducers being disposed such thatemitted ultrasonic pulses are orthogonalized in a measurement region inthe fluid pipe, reflected wave receivers for receiving ultrasonicechoes, which are reflected waves of the ultrasonic pulses emitted fromthe first and second ultrasonic transducers, respectively, from ameasurement region in the fluid pipe, velocity vector calculating meansfor calculating velocity vectors in an ultrasonic measurement linedirection from the intensity of the ultrasonic echoes received by thereflected wave receivers, and a flow velocity vector calculating meansfor calculating a flow velocity vector of a fluid to be measured from avector sum of the velocity vectors calculated by the velocity vectorcalculating means, wherein the flow rate of the fluid to be measured iscalculated from the flow velocity profile in the measurement linedirection in the fluid pipe calculated by the flow velocity vectorcalculating means.

As described above, the Doppler type ultrasonic flowmeter according tothe present invention is provided with the frequency selecting andsetting means for automatically selecting and setting oscillationfrequencies of ultrasonic pulses emitted from an ultrasonic transducer,and the incident angle adjusting and setting means for selectablysetting the incident angles of ultrasonic pulses emitted from theultrasonic transducer to optimum angles. According to this arrangement,it is possible to automatically set optimum frequencies or optimumincident angles of ultrasonic waves that cause the resonant transmissionphenomenon to take place with respect to the wall thickness of a fluidpipe. This obviates the need for providing an ultrasonic transducer thatis best suited to each type of fluid pipe. Thus, the Doppler typeultrasonic flowmeter is highly versatile and permits simple, easy,precise and highly accurate, contactless measurement of the flow rate ofa fluid to be measured that is flowing in the fluid pipe.

The Doppler type ultrasonic flowmeter in accordance with the presentinvention permits precise and highly accurate measurement of flow ratesfluids to be measured by utilizing ultrasonic Doppler shifts and alsopermits precise and highly accurate measurement even of opaque ortranslucent fluids, which cannot be measured by optical flow ratemeasuring means, or fluids having swirls, vortexes or non-parallel flowin a fluid pipe.

Furthermore, the above and other constructions and features of thepresent invention will be clearly understood from the followingdescription of embodiments given with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a first embodiment of a Doppler typeultrasonic flowmeter in accordance with the present invention.

FIG. 2 is a diagram for explaining a principle of an operation in flowrate measurement by the Doppler type ultrasonic flowmeter in accordancewith the present invention.

FIG. 3 is a diagram showing metal wall surface transmissioncharacteristics of ultrasonic waves.

FIG. 4 is a diagram showing average flow velocity profile of a fluid tobe measured that is flowing in a fluid pipe.

FIG. 5 is a diagram showing a second embodiment of the Doppler typeultrasonic flowmeter in accordance with the present invention.

FIG. 6 is an image diagram showing velocity components in an ultrasonicincident angle direction calculated on the basis of Doppler frequencies,which is used to explain a third embodiment of the Doppler typeultrasonic flowmeter in accordance with the present invention.

FIG. 7 is a figure of principle illustrating the third embodiment of theDoppler type ultrasonic flowmeter in accordance with the presentinvention.

FIG. 8 is a signal processing block diagram showing the third embodimentof the Doppler type ultrasonic flowmeter in accordance with the presentinvention.

BEST MODE FOR EMBODYING THE INVENTION

Embodiments of the Doppler type ultrasonic flowmeter in accordance withthe present invention will be explained hereunder with reference to theaccompanying drawings.

FIG. 1 is a diagram showing a first embodiment of the Doppler typeultrasonic flowmeter in accordance with the present invention. A Dopplertype ultrasonic flowmeter 10 measures flow velocity profile of a fluid12 to be measured, such as a liquid or gas, which is flowing in a fluidpipe 11 so as to perform time-dependent instant measurement of flowrates.

The Doppler type ultrasonic flowmeter 10 is provided with an ultrasonicvelocity profile measuring unit (hereinafter referred to as the “UVPunit”) 13 for performing contactless measurement of the fluid 12 to bemeasured that is flowing in the fluid pipe 11. The UVP unit 13 has anultrasonic transmitting means 15 for transmitting ultrasonic pulses ofpredetermined frequencies (fundamental frequency of f₀) along ameasurement line ML to the fluid 12, a fluid velocity profile measuringmeans 16 for receiving ultrasonic echoes of ultrasonic pulses enteringthe fluid 12, the echoes being the reflected waves from a measurementregion, to measure the flow velocity profile of the fluid 12 in themeasurement region, a computer 17, such as a microcomputer, a CPU, orMPU, functioning as a fluid flow rate computing means for performingarithmetic processing based on the flow velocity profile of the fluid 12to be measured to perform integration in a radial direction so as todetermine the flow rate of the fluid 12 in a time-dependent manner, adisplay device 18 allowing outputs from the computer 17 to be displayedin a time-series manner, and a frequency selecting and setting means 19for automatically selecting an ultrasonic wave of an optimum frequencyfor the fluid 12 that is flowing in the fluid pipe 11.

The ultrasonic transmitting means 15 has an ultrasonic transducer 20 foremitting ultrasonic pulses of required frequencies, and an oscillationamplifier 21 serving as a signal generator for oscillating theultrasonic transducer 20. The oscillation amplifier 21 is equipped withan oscillator 23 for generating electrical signals of predeterminedfundamental frequency f₀ and an emitter 24 (frequency F_(rpf)) foroutputting electrical signals in the form of pulses from the oscillator23 at predetermined time intervals (1/F_(rpf)). The pulse electricalsignals of the desired fundamental frequencies f₀ are input (inputted)from the oscillation amplifier 21 serving as the signal generator to theultrasonic transducer 20.

Upon the application of a pulse electrical signal to the ultrasonictransducer 20, an ultrasonic pulse of the fundamental frequency f₀ isemitted along the measurement line ML. The ultrasonic pulse is, forexample, a linear beam that has a pulse width of about 5 mm and hardlyspreads.

The ultrasonic transducer 20 serves also as a transmitter-receiver, andthe ultrasonic transducer 20 is adapted to receive ultrasonic echoes ofemitted ultrasonic pulses that are reflected by reflectors in the fluid.The reflectors are air bubbles evenly contained in the fluid 12 to bemeasured, particles of metal fine powder or the like, or foreign objectshaving different acoustic impedance from that of the fluid 12.

Ultrasonic echoes received by the ultrasonic transducer 20 are receivedby a reflected wave receiver 27 and converted into echo electricalsignals by the reflected wave receiver 27. The echo electrical signalsare amplified by an amplifier 28, and then subjected to digitizationthrough an A/D converter 29, and the digital echo signals are suppliedto a flow velocity profile measuring circuit 30 constituting the flowvelocity profile measuring means. The flow velocity profile measuringcircuit 30 receives a digitized electrical signal of the fundamentalfrequency f₀ from the oscillation amplifier 21 to measure changes in theflow velocity on the basis of the Doppler shift from the difference infrequency between the two signals and calculates the flow velocityprofile in the measurement region along the measurement line ML.Calibration of the flow velocity profile in the measurement region by atilt angle α makes it possible to measure the flow velocity profile inthe cross section of the fluid pipe 11.

Meanwhile, as the fundamental frequency f₀ of an ultrasonic pulseemitted from the ultrasonic transducer 20, an optimum value is selectedwith respect to the wall thickness of the fluid pipe 11 by the frequencyselecting and setting means 19 so as to develop a resonant transmissionphenomenon. It has been found that the metal wall transmissioncharacteristic of ultrasonic waves is extremely marked when the wallthickness of the fluid pipe 11 is the half or an integral multiple ofthe fundamental frequency f₀ of ultrasonic wave.

Based on this finding, the Doppler type ultrasonic flowmeter 10incorporates the frequency selecting and setting means 19 that permitsfree and automatic selection of the required fundamental frequencies f₀that cause various types of fluid pipes 11 to develop the resonanttransmission phenomenon without changing the thickness of the pipe wallof the fluid pipe 11.

The frequency selecting and setting means 19 has an oscillationamplifier 21 for causing the ultrasonic transducer to emit ultrasonicwaves of desired oscillation frequencies (fundamental frequencies f₀),an oscillation frequency changing device 31 that variably adjusts andsets the oscillation frequencies of the oscillation amplifier 21, afundamental frequency domain setting means 32 for operating theoscillation frequency changing device 31 within a range designatedbeforehand for the oscillation frequency changing device 31, forexample, in a frequency domain of 200 kHz to 4 MHz, a reflected wavereceiver 27 as the ultrasonic receiving means for receiving ultrasonicechoes reflected from a measurement region in the fluid pipe 11, areflected wave intensity extracting means 33, provided with a memory forthe intensities of the city that amplifies received ultrasonic echosignals by an amplifier 28, then extracts the intensities of theultrasonic echo signals and stores them in a memory provided for themeans 33, and a display device 18 equipped with a reflected waveintensity displaying function on which reflected intensities (ultrasonicecho intensities) extracted and stored by the reflected wave intensityextracting means 33 are displayed.

Thus, the frequency selecting and setting means 19 oscillates theultrasonic transducer 20 by the oscillation amplifier 21 to emitultrasonic pulses. The oscillation frequencies f₀ of the oscillationamplifier 21 are decided on the basis of the output (outputted) signalsof the oscillation frequency changing device 31. The oscillationfrequency changing device 31 variably sets the oscillation frequenciesof the oscillation amplifier 21 in the frequency domain decidedbeforehand by the fundamental frequency domain setting means 32.

The frequency selecting and setting means 19 repeatedly performsextraction and selection of ultrasonic oscillation frequencies by thecooperative action of the reflected wave intensity extracting means 33,the oscillation frequency changing device 31, etc., and automaticallyselects and sets an optimum ultrasonic frequency with respect to thewall thickness of the fluid pipe 11 that causes the resonanttransmission phenomenon.

When an optimum ultrasonic frequency is selected and set, an oscillationfrequency of the oscillation amplifier 21 is decided on the basis of anoutput signal from the oscillation frequency changing device 31. Theultrasonic transducer 20 is oscillated by the oscillation amplifier 21to emit an ultrasonic pulse of the desired fundamental frequency f₀,which is the optimum frequency, into the fluid pipe 11.

Since the ultrasonic pulse of the optimum frequency is emitted from theultrasonic transducer 20, an adequately reflected wave S/N ratio can besecured, and a large signal of the ultrasonic echo, which is thereflected wave, can be obtained. In order to secure the large ultrasonicecho signal, it is important to select the fundamental frequency f₀ ofan ultrasonic wave that causes the resonant transmission phenomenon totake place with respect to the wall thickness of the fluid pipe 11 (thewall thickness in the measurement line ML direction).

Setting the wall thickness of the fluid pipe 11 to an integral multipleof the half-wave length of an ultrasonic wave causes the ultrasonictransmittance in the interface of the fluid pipe 11 to markedly increasedue to resonant effect. As a result of the increased ultrasonictransmittance, the ultrasonic echo signal, which is the reflected wavefrom reflectors in the fluid to be measured 12, is enlarged.

Accordingly, if a fundamental frequency f₀ that is optimum for the wallthickness of the fluid pipe 11 is selected by the frequency selectingand setting means 19 as the oscillation frequency of the ultrasonicpulse to be emitted from the ultrasonic transducer 20, then attenuationin an ultrasonic path (travel path in the measurement line ML direction)decreases, while the ultrasonic transmittance in the interface of thefluid pipe 11 increases, thus making it possible to obtain adequateintensity of reflected waves.

In FIG. 1, reference numeral 35 denotes a contact medium for making iteasy for ultrasonic waves emitted from the ultrasonic transducer 20 tosmoothly enter into the fluid pipe 11. The contact medium 35 is providedto ensure good acoustic switching by reducing acoustic impedance emittedfrom the ultrasonic transducer 20 into the fluid pipe 11.

In the first embodiment, the ultrasonic echoes, which are reflectedwaves of ultrasonic pulses, have been received by the reflected wavereceiver 27. However, it is not always necessary to independently locatethe reflected wave receiver 27, and the reflected wave receiver mayalternatively be incorporated in the receiving function of theultrasonic transducer 20.

Referring now to FIG. 2 (2A, 2B and 2C), the working principle of theDoppler type ultrasonic flowmeter 10 will be explained.

As shown in FIG. 2A, when an ultrasonic pulse having the desiredfundamental frequency f₀ is emitted from the ultrasonic transducer 20,with the ultrasonic transducer 20 being installed at an angle α in thedirection in which a fluid to be measured flows with respect to theradial direction of the fluid pipe 11, the ultrasonic pulse is reflectedby reflectors, such as air bubbles or foreign matters, evenlydistributed in the fluid 12 to be measured on the measurement line MLand then returned to the ultrasonic transducer 20 in the form of anultrasonic echo a, which is a reflected wave, as shown in FIG. 2B.Reference character b in FIG. 2B denotes a multiplex reflected echo thatis reflected by the pipe wall on the side where the ultrasonic pulseenters, and reference character c denotes a multiplex reflected echothat is reflected by the pipe wall at the opposite side. The emittinginterval of ultrasonic pulses emitted from the ultrasonic transducer 20is 1/F_(rpf).

The echo signal emitted by the ultrasonic transducer 20 is subjected tofiltering treatment, and the flow velocity profile along the measurementline ML is measured by using the Doppler shift method. The measurementresult is shown in FIG. 2C. The flow velocity profile can be measured bythe fluid velocity profile measuring means 16 of the UVP unit 13.

The Doppler shift method applies the principle in which an ultrasonicpulse emitted into the fluid 12 flowing in the fluid pipe 11 isreflected by reflectors mixed or evenly distributed in the fluid 12 andturns into an ultrasonic echo, the frequency of the ultrasonic echobeing shifted by the magnitude proportional to flow velocity.

A flow velocity profile signal of the fluid 12, which is measured by theultrasonic fluid velocity profile measuring means 16, is sent to thecomputer 17 serving as the fluid flow rate computing means wherein theflow velocity profile signal is integrated in the radial direction ofthe fluid pipe 11 so as to time-dependently determine the flow rate ofthe fluid 12 to be measured. If the flow rate at the time t of the fluidto be measured 12 is denoted by m(t), then the flow rate can berepresented by an expression given below:m(t)=p∫v(x·t)·dA  (1)where p: Density of flow rate to be measured,

-   -   -   v(x·t): Velocity component at time t (x direction).

From expression (1), the flow rate m(t) at the time t in the fluid pipe11 can be rewritten to an expression given below:m(t)=p∫∫vx(r·θ·t)·r·dr·dθ  (2)where vx(r·θ·t): Velocity component in the direction of the pipe axis atangle θ and distance r from the center on the cross section of the pipeat the time t.

From this expression (2), the Doppler type ultrasonic flowmeter 10 iscapable of obtaining the space profile of a flow of the fluid to bemeasured 12 instantly at a response speed of, for example, about 50 msecto about 100 msec. The flow of the fluid 12 in the fluid pipe (roundpipe) 11 has a three-dimensional profile in an unsteady state if anadequate runup zone cannot be secured or temporal fluctuation is presentdue to opening/closing of a valve or start/stop of a pump. The Dopplertype ultrasonic flowmeter 10, however, allows a flow velocity profile ina measurement region to be time-dependently determined at once, so thatthe flow rate of the fluid 12 to be measured can be precisely determinedwith high accuracy independently of whether the flow is in a steady orunsteady state.

Furthermore, a confirmatory test on the transmission characteristics ofultrasonic waves emitted from the ultrasonic transducer 20 was conductedby using the Doppler type ultrasonic flowmeter 10 in accordance with thepresent invention.

FIG. 3 shows test results showing the wall surface transmissioncharacteristics of the ultrasonic waves.

The Doppler type ultrasonic flowmeter 10 used for this test was adaptedto be able to automatically adjust and set the fundamental frequenciesof the ultrasonic waves emitted from the ultrasonic transducer 20 in,for example, units of 5 kHz from 200 kHz to a few MHz, e.g., 2 MHz, bythe frequency selecting and setting means 19.

In order to carry out the test on the wall surface transmission ofultrasonic waves, stainless steel was embedded in a portion of anacrylic pipe having a diameter of 250 mmφ, and the ultrasonic transducer20 was installed on the outer portion of the stainless steel wall.Ultrasonic waves were emitted, and the reflection intensity of theultrasonic waves from an opposing wall surface of the acrylic pipe waschecked at different fundamental frequencies. Reflected wavetransmission intensity curves h, i and j obtained when the fundamentalfrequency was changed in the units of 5 kHz are shown.

For the test on the wall surface transmission of the ultrasonic waves,three different wall thicknesses, 9.5 mm, 11.5 mm, and 13 mm, ofstainless wall were used. FIG. 3 shows the example of the ultrasonicwave wall surface transmission test using the stainless steel wallthickness of 9.5 mm. The axis of abscissa indicates the fundamentalfrequency f₀ of ultrasonic waves, while the axis of ordinates indicatesthe reflection intensity of ultrasonic waves from the opposing wall. Thecharacteristic frequencies of the three types of the ultrasonictransducers used are 0.25 MHz, 0.5 MHz and 1 MHz, the transmissionintensity curves thereof being denoted by reference characters h, i andj.

In FIG. 3, arrows 1, m, and n denote the relationships between theoscillation frequency wavelengths of ultrasonic waves and the stainlesssteel wall thicknesses, and indicate the positions of the frequencies of½-fold, 1-fold, and {fraction (3/2)}-fold stainless steel wallthicknesses, beginning with a lowest ultrasonic wavelength.

Based on FIG. 3, it is understood that, if, for example, a 1-MHzultrasonic transducer is used, then good transmission characteristic ofultrasonic waves is obtained when the flow rate measurement is performedby setting the fundamental frequency to approximately 910 kHz accordingto the wall thickness of a stainless steel pipe. It is seen that thefrequency transmission intensity curve j shows a high transmissionintensity level of reflected waves at the position indicated by thearrow n.

Based now on the transmission characteristics of the ultrasonic wavesshown in FIG. 3, a fluid pipe made of carbon steel (internal diameter of150 mm) having a wall thickness of 9.5 mm was prepared, the ultrasonictransducer 20 of 1-MHz characteristic frequency was used, and thefundamental frequency f₀ emitted from the ultrasonic transducer 20 wasselected and set to 910 kHz by the frequency selecting and setting means19 to measure the flow velocity profile of the fluid to be measured.

The results of the temporal average flow velocity profile of the fluidto be measured obtained by the measurement test are shown in FIG. 4. Themeasurement points of the flow velocity profile of the fluid ranged from60 mm to 150 mm. On the side before the pipe central portion (range of 0mm to 60 mm) of the fluid pipe made of carbon steel, the reflection ofultrasonic waves in the wall made it difficult to obtain an adequateflow velocity profile. In the measurement region on the side beyond thepipe central portion, however, the wall surface did not affect the flowvelocity profile of the fluid 12 to be measured, allowing a relativelysmooth average flow velocity profile curve “O” to be obtained.

Based on the average flow velocity profile curve “O”, the average flowvelocity profile is integrated in the fluid pipe 11 so as to make itpossible to perform accurate, contactless measurement of the flow rateof the fluid 12 flowing in the fluid pipe 11.

FIG. 5 shows a second embodiment of the Doppler type ultrasonicflowmeter in accordance with the present invention.

A Doppler type ultrasonic flowmeter 10A shown in this embodiment may beadapted to change the wall thickness of a fluid pipe 11 to induce theresonant transmission phenomenon as a method to improve the S/N ratio ofreflected waves in place of selecting an optimum frequency of anultrasonic pulse entering the fluid pipe 11.

However, since it is actually impossible to change the wall thickness ofthe fluid pipe 11, a means equivalent to changing the wall thickness ofthe fluid pipe 11 has been provided by changing the mounting angle of anultrasonic transducer 20.

In the second embodiment, an incident angle α of the ultrasonic pulsesemitted from the ultrasonic transducer 20 is adjusted and set by anincident angle adjusting and setting means 40 thereby to automaticallyselect the incident angle of an ultrasonic wave which corresponds to thewall thickness of the fluid pipe 11. The like reference numerals areadded to the members corresponding to those of the Doppler typeultrasonic flowmeter 10 described with reference to the first embodimentassigned by the same reference numerals, and the explanation thereofwill be omitted herein.

The Doppler type ultrasonic flowmeter 10A shown in FIG. 5 is providedwith the incident angle adjusting and setting means 40 in place of thefrequency selecting and setting means 19.

The incident angle adjusting and setting means 40 is equipped with anultrasonic transducer 20 provided on the fluid pipe 11 from outside in amanner that its mounting angle can be adjusted, an incident anglechanging mechanism 41 capable of adjusting and setting an incident angleα of an ultrasonic pulse emitted from the ultrasonic transducer 20, anincident angle range setting means 43 for actuating the incident anglechanging mechanism 41 in an incident angle range designated beforehand,e.g., the incident angle α can be changed within a range of angle scopewidth of 5 degrees to 45 degrees, and a reflected wave intensityextracting means 44 which receives an ultrasonic echo reflected from ameasurement region in the fluid pipe 11 and then extracts and stores theintensity of the ultrasonic echo. The ultrasonic echo intensityextracted and stored by the reflected wave intensity extracting means 44is then displayed on a display unit 18 provided with a reflected waveintensity display function.

The incident angle adjusting and setting means 40 is a mechanism forcausing the incident angle changing mechanism 41 to change the incidentangle α of the ultrasonic waves in a range of about 5 degrees to about45 degrees. Based on an output signal issued from the incident anglechanging mechanism 41, the mounting angle of the ultrasonic transducer20 is automatically adjusted and set to an optimum value. The mountingangle of the ultrasonic transducer 20 is variably adjusted and set bydriving a mounting angle changing and adjusting mechanism, such as astepping motor 46 or the like, by an output signal issued from theincident angle changing mechanism 41.

The incident angle α of the ultrasonic wave emitted from the ultrasonictransducer 20 is the angle formed with respect to a perpendicular lineor a perpendicular surface of the pipe surface of the fluid pipe 11. Theincident angle of the ultrasonic pulses emitted from the ultrasonictransducer 20 are set to optimum angles by the incident angle adjustingand setting means 40 with respect to the wall thickness of the fluidpipe 11 so as to cause a resonant transmission phenomenon to take place.

The incident angle adjusting and setting means 40 changes the incidentangles of the ultrasonic pulses emitted from the ultrasonic transducer20 in an angle range of the incident angles from about 5 degrees toabout 45 degrees by the output signals from the incident angle changingmechanism 41 and the reflected wave intensities are extracted and storedby the reflected wave intensity extracting means 44. The reflected waveintensities stored by the reflected wave intensity extracting means 44are displayed by the display unit 18, while an operation of extractingand selecting the incident angles of the ultrasonic pulses is repeatedlyperformed by the incident angle adjusting and setting means 40 toautomatically select and adopt the optimum incident angles of theultrasonic pulses.

Adjusting and setting of the incident angles of the ultrasonic pulsesemitted from the ultrasonic transducer 20 to optimum angles by theincident angle adjusting and setting means 40 will become equivalent tothe physical change of the wall thickness of the fluid pipe 11, and theultrasonic pulses emitted from the ultrasonic transducer 20 make itpossible to perform precise and accurate measurement of the flowvelocity profile and the flow rate of the fluid 12 to be measuredflowing in the fluid pipe 11.

The propagation distances in materials, that is, the propagationdistances of the ultrasonic waves in the fluid pipe 11, are changed bychanging the incident angles (entering angles) of ultrasonic wavesemitted from the ultrasonic transducer 20. Furthermore, the setting ofthe propagation distances of the ultrasonic waves to the integralmultiples of half-wave lengths of ultrasonic waves causes the resonanttransmission phenomenon to take place with respect to the wall thicknessof the fluid pipe 11. This makes it possible to secure an adequatereflected wave S/N ratio, allowing the intensity of an ultrasonic echo,which is a reflected wave, to be secured. Hence, the flow velocityprofiles and flow rates of fluids to be measured flowing in the fluidpipe 11 can be measured accurately and contactlessly.

In each of the described embodiments of the Doppler type ultrasonicflowmeter, there are shown the example equipped with the frequencyselecting and setting means 19 and the example equipped with theincident angle adjusting and setting means 40 have been shown.Alternatively, however, in a single Doppler type ultrasonic flowmeter,the frequency selecting and setting means 19 and the incident angleadjusting and setting means 40 may be combined. The Doppler typeultrasonic flowmeter equipped with the combination of the two settingmeans 19 and 40 permits easy automatic selection and setting of optimumfrequencies and optimum incident angles.

The Doppler type ultrasonic flowmeters 10 and 10A shown in FIG. 1 toFIG. 4 are adapted to measure the flow rates of fluids to be measured bythe linear measurement method of flow velocity profiles, which utilizesthe ultrasonic pulse and the ultrasonic echo Doppler shifts.Accordingly, in order to improve measurement accuracy, the number ofmeasurement lines ML and the number of ultrasonic transducers 20 to beinstalled must be increased. In practice, an N number of the ultrasonictransducers 20 will be required to be installed in predeterminedintervals in the circumferential direction of the pipe 11, and themeasurement lines ML are set at an angle α with respect to the normal tothe pipe wall so that all the measurement lines ML pass the axis of thepipe 11.

Accordingly, if the flow of the fluid 12 passing in the pipe 11 isflowing in the direction of the pipe axis and a flow v_(r) in the radialdirection and a flow v_(θ) at an angle θ can be ignored, thenv_(x)>>v_(r), v_(x)>>v_(θ). the flow rate measurement will be simplifiedand represented by an expression given below: $\begin{matrix}{{m(t)} = {\sum\limits_{i}^{N}\quad{{\cdot \frac{2\pi}{N}}{\int_{- R}^{R}{\left\{ {{{{vx}\left( {{r \cdot \theta}\quad{i \cdot t}} \right)}/\sin}\quad\alpha} \right\} \cdot r \cdot \quad{\mathbb{d}r}}}}}} & (3)\end{matrix}$

Thus, the determined flow rate of the fluid 12 can be instantlydisplayed by the display unit 18 in the time-dependent manner. Thedisplay unit 18 is also capable of displaying the flow velocity profilesalong the measurement lines ML of the fluid 12 in the fluid pipe 11 orthe flow velocity profiles in the cross section of the pipes.

FIG. 6 to FIG. 8 show a third embodiment of the Doppler type ultrasonicflowmeter in accordance with the present invention.

As illustrated in FIG. 6, a Doppler type ultrasonic flowmeter 10B ofthis embodiment calculates, on the basis of a Doppler frequency, avelocity component V2 in the direction of an ultrasonic wave incidentangle (entering angle) of a fluid 12 to be measured which is flowing ina fluid pipe 11. From the calculated Doppler frequency, the flowvelocity profile along a measurement line ML is determined according toa linear measurement method so as to calculate the flow rate of thefluid 12.

The Doppler type ultrasonic flowmeter 10B calculates the velocity vectorV2 in the direction of an ultrasonic path (the measurement line ML) fromthe Doppler frequency and divides the velocity vector V2 by sin α so asto calculate the velocity vector V1 in the axial direction of the fluidpipe 11.

The Doppler type ultrasonic flowmeter 10B cannot calculate correct flowvelocities if the flow of the fluid 12 to be measured is not parallel tothe fluid pipe 11 and a swirling flow is present in the fluid pipe 11 ora non-parallel flow is present in the fluid pipe 11. For example, asshown in FIG. 7, if there is an air bubble having a velocity vector V3,the velocity vector V3 then shares the velocity vector V2 in the samedirection as that of the velocity vector V1 of the fluid 12, so that theflowmeter erroneously calculates the apparent velocity of the air bubblein the fluid 12 as the large velocity in the axial direction of thefluid pipe 11.

In order to solve the problem of calculating the flow rates based on theapparent velocities, the Doppler ultrasonic flowmeter 10B is providedwith two ultrasonic transducers 20 and 20 a mounted on the fluid pipe11. The one ultrasonic transducer 20 is installed so as to be orthogonalwith respect to the other ultrasonic transducer 20 a. The two ultrasonictransducers 20 and 20 a determine their velocity vectors V2 and V4, andthe sum of the velocity vectors V2 and V4 is calculated, thereby makingit possible to properly determine the flow velocity of the fluid 12 tobe measured and the flow velocity of the air bubble.

In the Doppler type ultrasonic flowmeter 10B, the other ultrasonictransducer 20 a is configured to be movable on the fluid pipe 11 inrelation to the one ultrasonic transducer 20 in order to properlymeasure the flow velocity of the fluid 12.

Hence, the Doppler type ultrasonic flowmeter 10B is equipped with anultrasonic transducer moving mechanism 46 for relatively moving theother ultrasonic transducer 20 a towards or backward with respect to theone ultrasonic transducer 20 and is configured as illustrated in thesignal processing block diagram shown in FIG. 8.

In the Doppler type ultrasonic flowmeter 10B shown in FIG. 8, the twoultrasonic transducers 20 and 20 a are disposed such that the incidentdirections of the ultrasonic pulses emitted from the two ultrasonictransducers 20 and 20 a are orthogonalized with each other in the fluidpipe 11. More specifically, in the Doppler type ultrasonic flowmeter10B, the two ultrasonic transducers 20 and 20 a are disposed such thatthe ultrasonic pulses emitted from the two ultrasonic transducers 20 and20 a are orthogonalized in a measurement region in the fluid pipe 11.

The Doppler type ultrasonic flowmeter 10B is equipped with reflectedwave receivers 27 and 27 a for receiving ultrasonic echoes, which arereflected waves of the ultrasonic pulses emitted from the two ultrasonictransducers 20 and 20 a, from a measurement region in the fluid pipe 11,velocity vector calculating means 47 and 47 a for calculating thevelocity vectors in the directions of the ultrasonic measurement linesfrom the intensities of the ultrasonic echoes received by the respectivereflected wave receivers 27 and 27 a, and a flow velocity vectorcalculating means 48 for calculating the flow velocity vector of a fluidto be measured from the vector sum of the velocity vectors calculated bythe respective velocity vector calculating means 47 and 47 a, whereinthe flow rate of the fluid 12 is calculated from a flow velocity profilein the direction of a measurement line ML in the fluid pipe 11 which iscalculated by the flow velocity vector calculating means 48.

The ultrasonic echoes, which are the reflected waves of the ultrasonicpulses emitted from the two ultrasonic transducers 20 and 20 a and whichare reflected from the measurement region in the fluid pipe 11, arereceived by the reflected wave receivers 27 and 27 a, respectively. Theintensity signals of the ultrasonic echoes received by the respectivereflected wave receivers 27 and 27 a are converted into velocity vectorsin the directions of the measurement lines ML (the directions of paths)by the velocity vector calculating means 47 and 47 a. The vector sum ofthe obtained velocity vectors in the directions of paths is calculatedby the flow velocity vector calculating means 48 so as to calculate acorrect velocity vector of the flow velocity of the fluid 12 to bemeasured.

The flow rates of the fluid 12 can be determined by configuring the flowvelocity profile measuring circuit 30 by using the velocity vectorcalculating means 47, 47 a and the flow velocity vector calculatingmeans 48, or by measuring the flow velocity profile of the fluid 12 tobe measured flowing in the fluid pipe 11 along the directions of paths(measurement lines) ML and then performing a computation for integratingthe flow velocity profile in the directions of paths of ultrasonicwaves.

After the flow velocity at the position of the flow velocity vectorcalculating means 48 of the flow velocity profile measuring circuit 30is calculated, the ultrasonic transducer 20 or 20 a is moved on thefluid pipe 11 by the ultrasonic transducer moving mechanism 46 tocollect data at a next position. The ultrasonic transducers 20 and 20 aare moved from one position to another by the ultrasonic transducermoving mechanism 46 to determine the flow velocity profile of the fluidto be measured 12 over a whole area in the directions of paths of theultrasonic pulses. This allows the flow rate to be precisely determinedthrough the computation.

INDUSTRIAL APPLICABILITY

The Doppler type ultrasonic flowmeter in accordance with the presentinvention makes it possible to automatically set optimum frequencies andoptimum incident angles of the ultrasonic waves with respect to the wallthickness of a fluid pipe which causes a resonant transmissionphenomenon to take place, obviates the need for providing an ultrasonictransducer optimum for each type of fluid pipe, features the highversatility, and permits the simple, easy, precise, accurate andcontactless measurement of the flow rate of the fluid to be measuredthat is flowing in the fluid pipe.

Moreover, the Doppler type ultrasonic flowmeter in accordance with thepresent invention permits the precise and highly accurate measurement ofthe flow rate of the fluid to be measured by utilizing the Dopplershifts of the ultrasonic waves and also permits the precise and highlyaccurate measurement even of opaque or translucent fluids, which cannotbe measured by optical flow rate measuring means, or the fluids havingswirls, vortexes or non-parallel flow in the fluid pipe, thus showinghigh industrial applicability.

1. A Doppler type ultrasonic flowmeter, comprising: an ultrasonictransmitting means provided with an ultrasonic transducer for emittingultrasonic pulses and adapted to direct the ultrasonic pulses from theultrasonic transducer into a fluid to be measured that is flowing in afluid pipe; a flow velocity profile measuring means for receiving anultrasonic echo of the ultrasonic pulses entered into the fluid to bemeasured, said ultrasonic echo being reflected from a measurement regionin the fluid pipe and measuring a flow velocity profile of the fluid tobe measured in the measurement region; a fluid flow rate computing meansfor calculating the flow rate of the fluid to be measured on the basisof the flow velocity profile of the fluid to be measured; and afrequency selecting and setting means for automatically selecting afundamental frequency of an ultrasonic wave from the ultrasonictransducer that causes a resonant transmission phenomenon to take placewith respect to a pipe wall of the fluid pipe, wherein said frequencyselecting and setting means controls the operation of the ultrasonictransmitting means so that an ultrasonic wave of a selected optimumfrequency is emitted from the ultrasonic transducer.
 2. The Doppler typeultrasonic flowmeter according to claim 1, wherein said oscillationfrequency selecting and setting means automatically adjusts and sets theoscillation frequency of an ultrasonic pulse emitted from the ultrasonictransducer so that an integral multiple of an ultrasonic wave half-wavelength is equal to the wall thickness of the fluid pipe.
 3. The Dopplertype ultrasonic flowmeter according to claim 1, wherein said oscillationfrequency selecting and setting means comprises an oscillation amplifierfor emitting an ultrasonic wave of a required oscillation frequency fromthe ultrasonic transducer, an oscillation frequency changing device forvariably adjusting and setting an oscillation frequency of theoscillation amplifier, a frequency domain setting means for operatingthe oscillation frequency changing device in a frequency domaindesignated beforehand, an ultrasonic receiving means for receiving anultrasonic echo of the ultrasonic pulse emitted from the ultrasonictransducer that is reflected from the measurement region in the fluidpipe, and a reflected wave intensity extracting means for extracting andstoring the intensity of the received ultrasonic echo, and wherein saidoscillation frequency selecting and setting means repeats an operationof extracting and selecting oscillation frequencies to automaticallyselect an optimum frequency of an ultrasonic wave.
 4. The Doppler typeultrasonic flowmeter according to claim 1, further comprising anincident angle adjusting and setting means for adjusting and setting anincident angle of an ultrasonic pulse emitted from the ultrasonictransducer into the fluid to be measured, wherein the incident angleadjusting and setting means has the ultrasonic transducer provided onthe fluid pipe so as to be adjusted and set to provide the ultrasonicpulse with an incident angle that causes the resonant transmissionphenomenon to take place with respect to the pipe wall of the fluidpipe, said frequency selecting and setting means and said incident angleadjusting and setting means being combined.
 5. A Doppler type ultrasonicflowmeter comprising: an ultrasonic transmitting means provided with anultrasonic transducer emitting ultrasonic pulses and adapted to directultrasonic pulses from the ultrasonic transducer into a fluid to bemeasured that is flowing in a fluid pipe; a fluid velocity profilemeasuring means for receiving an ultrasonic echo of the ultrasonicpulses entered into the fluid to be measured that is reflected from themeasurement region in the fluid pipe and measuring a flow velocityprofile of the fluid to be measured in the measurement region; a fluidflow rate computing means for calculating the flow rate of the fluid tobe measured on the basis of the flow velocity profile of the fluid to bemeasured; and an incident angle adjusting and setting means foradjusting and setting the incident angle of an ultrasonic pulse from theultrasonic transducer into the fluid to be measured, wherein saidincident angle adjusting and setting means has the ultrasonic transducerprovided on the fluid pipe so as to be adjusted and set to provide theultrasonic pulse with an incident angle that causes the resonanttransmission phenomenon to take place with respect to the pipe wall ofthe fluid pipe.
 6. The Doppler type ultrasonic flowmeter according toclaim 5, wherein said incident angle adjusting means comprises anultrasonic transducer provided on the fluid pipe from an outer side, anincident angle changing mechanism that permits adjustment and setting ofthe incident angle of an ultrasonic pulse emitted from the ultrasonictransducer, an incident angle range setting means for actuating theincident angle changing mechanism within the range of an incident anglescope designated beforehand, and a reflected wave intensity extractingmeans for receiving an ultrasonic echo of the ultrasonic pulse emittedfrom the ultrasonic transducer which is reflected from the measurementregion in the fluid pipe, and then extracting and storing the intensityof the ultrasonic echo, wherein said incident angle adjusting andsetting means repeatedly perform an operation for extracting andselecting ultrasonic pulse incident angles so to automatically select anoptimum ultrasonic pulse incident angle.
 7. The Doppler type ultrasonicflowmeter according to claim 5, wherein said ultrasonic transducer isprovided on the outer side of the fluid pipe so that the mounting anglethereof is adjusted, and the mounting angle of the ultrasonic transduceris selected by the incident angle changing mechanism so as to adjust andset the incident angle of an ultrasonic pulse emitted from theultrasonic transducer.
 8. A Doppler type ultrasonic flowmetercomprising: a first ultrasonic transducer provided on a fluid pipe; asecond ultrasonic transducer provided apart from the first ultrasonictransducer in an axial direction of the fluid pipe; an ultrasonictransducer moving mechanism for relatively moving the first ultrasonictransducer forward or backward with respect to the second ultrasonictransducer, said two ultrasonic transducers being disposed such thatemitted ultrasonic pulses are orthogonalized in a measurement region inthe fluid pipe; reflected wave receivers for receiving ultrasonicechoes, which are reflected waves of the ultrasonic pulses emitted fromthe first and second ultrasonic transducers, respectively, from ameasurement region in the fluid pipe; velocity vector calculating meansfor calculating velocity vectors in ultrasonic measurement linedirections from the intensities of the ultrasonic echoes received by thereflected wave receivers; and a flow velocity vector calculating meansfor calculating a flow velocity vector of a fluid to be measured from avector sum of the velocity vectors calculated by the velocity vectorcalculating means, wherein the flow rate of the fluid to be measured iscalculated from the flow velocity profile in the measurement linedirection in the fluid pipe calculated by the flow velocity vectorcalculating means.